The field of the invention relates generally to turbine engines and, more particularly, to systems and methods for use in operating turbine engines.
At least some known turbine engines are used in cogeneration facilities and power plants. Some of such turbine engines may have high specific work and power per unit mass flow requirements. To increase the operating efficiency, at least some known turbine engines are operated with increased combustion temperatures, as engine efficiency generally increases as combustion gas temperatures increase.
However, operating with higher temperatures may also increase the generation of polluting emissions, such as carbon monoxide (CO) and oxides of nitrogen (NOx). To reduce the generation of such emissions, at least some known turbine engines include combustion system designs and/or the use of other technology systems that are designed to reduce such emissions. For example, at least some turbine engines include a selective catalytic reduction (SCR) device on an exhaust system of the turbine engine. SCRs have been shown to reduce NOx emissions from Gas Turbine to approximately 2-3 ppm in the exhaust. However, SCR devices can be costly to install and to operate. Moreover, known SCR devices require expensive process chemicals, such as anhydrous ammonia, on a continuous basis to function. Because SCR devices also carry the environmental risk of ammonia emission as a by-product of their operation, many countries prohibit the use of ammonia-based SCR devices. In such countries, turbine operators must operate the turbine engines with firing temperatures that are below intended design ratings to achieve emissions compliance. Delivering approximately 2-3 ppm of NOx emissions from the gas turbine exhaust is difficult due to Lean Blow Out (LBO) concerns in the Gas Turbine Combustor using even the best available premixing technology.
Reduced levels of NOx emissions in turbine engines may also be achieved using known premixing technology, along with Dry Low NOx (DLN) combustion systems. For example, at least some known DLN combustion systems include multiple premix fuel circuits and/or fuel nozzles to reduce NOx emissions at a given cycle temperature. If the combustor can produce the target 2-3 ppm of NOx emissions at the desired cycle temperature, the machine can deliver the target output and performance. There is still, however, the issue of flame stability and LBO when running at such low NOx levels. Stability and LBO can be addressed with a process known as hydrogen doping. In a hydrogen doping process, hydrogen gas (H2) is mixed with fuel prior to the fuel and hydrogen gas mixture being channeled to the fuel nozzles. Hydrogen doping has been shown to reduce emission levels and helps reduce a combustor lean blow out (LBO). However, the addition of hydrogen gas may actually increase NOx levels at a given cycle temperature. The effect is that in order to obtain a lower NOx level, the combustor exit temperature must be decreased. However, reducing the temperature within the combustor may result in decreasing the output of the turbine engine and/or decreasing the efficiency of the turbine engine. Moreover, hydrogen gas can be very expensive for use with all the fuel nozzles.